Doctors used a disabled form of HIV to reprogram a child's immune system to kill her cancer. Emma Whitehead had been battling leukemia for two years and has now been in remission for seven months thanks to the groundbreaking medical treatment.

"Different to using chemotherapy to achieve those goals, you take out some of the body's immune cells and you basically reprogram them. You put some genetic material into them that teaches the cells to attack that cancer," says Dr. Sanjay Gupta. "They're using a sort of deadened form of the HIV virus to transport that genetic material into cells."

The experimental procedure was developed by researchers at the University of Pennsylvania, and they've tested it on 12 patients so far with varying results. The $20,000 price tag is cheaper than a bone marrow transplant.

Explaining the science behind the body's reaction, Gupta says, "The person also, often times, gets very sick. They get the immune system really blown up. It's a long hospitalization, it's a tough hospitalization."

Gupta also points to the possible implications for patients who relapse. "If you have these cells in your body that are now trained to be able to recognize that cancer, if the cancer were to ever come back, it is possible these cells could immediately attack it. So it's kind of, almost like a cancer vaccine....imagine that."